I've set up a page at http://bahai9.com/wiki/Joshua_%28person%29
with the quotations in the Writings that I could find with a quick search.
My impression is that the battles were surely symbolic, just as the miracles of Moses appear to be interpreted that way (for some example arguments as to why, see the paragraph beginning "Bahá'u'lláh did not comment on Moses's miracles directly"... in Dr. Robert Stockman's work "Notes on Judaism from a Baha'i Perspective", at http://bahai-library.com/stockman_notes_judaism
You might also like to see http://en.bahaitext.org/Star_of_the_Wes ... e_10#pg196
where 'Abdu'l-Baha, though encouraging Jews of that time to return to Israel in fulfillment of Old Testament prophecy, also advises the need for their mingling with other races and develop the country for all.